.box {
  width: 800px;
  border: 10px solid blue;
  margin: 0 auto;
}

.one {
  float: left;
  width: 300px;
  height: 200px;
  background-color: purple;
}

.two {
  float: left;
  width: 200px;
  height: 200px;
  background-color: pink;
}
.box::after{
  content: "";
  clear: both;
  display: table;
}

.footer {
  height: 200px;
  background-color: green;
}

